The present invention relates to a chemical-resistant wholly aromatic polyamide fiber material. More particularly, the present invention relates to a wholly aromatic polyamide fiber material having an enhanced resistance to chemicals such as alkali and acid, and also to heat.
It is known that the so-called wholly aromatic polyamide resins have higher softening and melting points than those of aliphatic polyamide resins, and exhibit desirable physical and chemical properties, such as: excellent heat-resisting properties, for example, a high ratio of mechanical strength at an elevated temperature compared to that of at room temperature, superior stabilities in dimension and shape at an elevated temperature, and a high resistance to thermal decomposition; high resistances to various chemicals, and, superior mechanical properties, for example, a high tensile strength and high Young's moduls. Also, it is known that the wholly aromatic polyamide resins have high orienting and crystallizing properties. Accordingly, the wholly aromatic polyamide resins are suitable as a material for producing filaments, fibers and films having a high heat resistance, a superior flame-retarding property, and high tensile strength and Young's modulus.
Also, it is known that in various types of industires, various types of fluids (gases and liquids) are filtered with filter cloths. The fluids to be filtered sometimes have an elevated temperature and/or contain various chemicals, for example, acid substances such as hydrogen chloride (hydrochloric acid), sulfur dioxide (sulfurous acid anhydride), sulfur trioxide (sulfuric acid anhydride) and sulfuric acid, and alkaline substances such as sodium hydroxide and potassium hydroxide. Therefore, the filter cloth should exhibit satisfactory resistance not only to elevated temperatures, but also, to various chemicals, in addition to having a satisfactory filtering property.
In view of the above-mentioned preferable properties of the wholly aromatic polyamide resins, it is expected that the wholly aromatic polyamide fibers are useful for producing a filter cloth suitable for filtering various fluids having an elevated temperature and containing various chemicals.
Hitherto, the filter cloth resistant to heat and chemicals were produced from inorganic fibers, for example, glass fibers or asbestos fibers, or synthetic organic fibers, for example, polyethylene terephthalate fibers or poly-m-phenylene isophthalate fibers. The glass fibers and asbestos fibers are highly resistant to heat and acid substances. However, the glass fibers exhibit an unsatisfactory resistance to alkaline substances, a poor filtering property to dust and a large flexural fatigue. The polyethylene terephthalate fiber cloth exhibits an excellent filtering property and resistance to flexural fatigue. However, the polyethylene terephthalate fiber cloth is unsatisfactory in its resistance to acid and alkaline substances and heat. Also, the wholly aromatic polyamide fiber cloth has an excellent filtering property and excellent resistances to heat, flexural fatigue and alkaline substances. However, the filtering cloth consisting of wholly aromatic polyamide fibers such as poly-m-phenylene isophthalate fibers exhibits an unsatisfactory resistance to acid substances.
In order to enhance the resistance of the wholly aromatic polyamide fiber cloth to the chemicals, various types of treatments on the wholly aromatic polyamide fiber cloth were attempted. However, the attempted treatments not only failed to impart a satisfactory resistance to chemicals to the wholly aromatic polyamide fiber cloth, but also, caused the filtering property of the cloth to become remarkably poor.
Accordingly, it is strongly desired to enhance the resistance of the wholly polyamide fiber material to chemicals without degrading another properties thereof, for example, the filtering property, resistance to heat or the mechanical strength thereof.